Pyrolysis of Self-Assembled Iron Porphyrin on Carbon Black as Core/Shell Structured Electrocatalysts for Highly Efficient Oxygen Reduction in Both Alkaline and Acidic Medium

Abstract

A simple carbonization of evaporation-induced self-assembled iron(III) porphyrin (FeP) layers uniformly coated on carbon black, leading to an unprecedented core/shell structured nonprecious metal electrocatalysts (NPMEs) composed of N-doped graphene-like layers uniformly coated on carbon is reported. The thickness of graphene-like shell can be readily adjusted up to about 6.6 nm by varying the amount of FeP loaded on carbon. Interestingly, the obtained NPME exhibits one of the highest oxygen reduction reaction (ORR) activity in both alkaline (half-wave potential of 0.87 V vs reversible hydrogen electrode-RHE) and acidic (half-wave potential of 0.75 V vs RHE) medium. In particular, the core/shell structured NPME demonstrates a remarkable durability in acidic conditions superior to that of commercial Pt/C, which likely comes from the exposure of inner active sites after the outermost layer is consumed. Furthermore, the core/shell NPME displays direct 4e and indirect 4e process toward ORR in alkaline and acidic medium, respectively. This study points out a new avenue for the design of high-performance NPMEs in both alkaline and acidic media, which may have potential applications in polymer electrolyte membrane fuel cells (PEMFCs), metal-air batteries, and electrolyzers.